This invention relates to a process and apparatus suitable for use in packing commodities in bags of heat sealable plastics material. Such commodities include animal carcasses or parts of animal carcasses or joints such as bacon joints. It is particularly useful in, but not limited to, packing meat such as beef or bacon, or cheese, in vacuum packs.
Such packing has been in use for some time usually using a shrink film i.e. a thermoplastics film made under tension and set when cold, but which when heated (for example in hot water up to 100.degree. C.) will release its inherent shrink characteristics so that the film shrinks and collapses onto the commodities in the bags. This process has been used mainly for bacon joints which are bagged, and sealed under vacuum in a hood-type vacuum apparatus forming an unheated chamber when closed, in which the open bag mouth is sealed by conventional means e.g. impulse sealing when the bag is under vacuum in the chamber and surplus film is cut off by a knife or hot wire. The chamber is vented to atmosphere and the bag is moved on a conveyor and immersed in a hot water dip tank whereupon the bag material shrinks taut around the commodity due to the release of the shrink characteristics of the bag material. The sealed shrink bags are conveyed to a drying zone and allowed to dry so that appropriate labelling can be applied to the bags.
Such know processes are expensive in the initial equipment costs especially the dip tank, drying and drainage means and conveyors. Moreover the operational costs, costs of bag materials and maintenance costs are undesirably high and the requisite apparatus and equipment occupy large floor space. The running costs include power for heating the dip tank and for running the conveyors. A disadvantage of the known process is that when the bags are sealed during application of vacuum to the bag interiors, the bag material at the bag mouth creases and fat and grease tend to be sucked into the bag mouth seal area so that a high rate of incidence of leaking bags results which increases the running costs and reduces output levels.
In another known process a nylon/polyethylene laminate non-shrink bag material is used in which, when the filled bag is impulse sealed under vacuum as in the aforesaid process then on venting the hood chamber to atmospheric pressure conditions, the bag collapses onto the product in the bag in an unshrunk wrinkled condition in contact with the surface of the product. The sealed bag is then passed on a moving conveyor through a tunnel in which hot air causes all-over sealing of the free bag material i.e. the bag material which is not in contact with the product in the bag. This process suffers from the same disadvantages as the known shrink process referred to above and in addition the tunnel heat e.g. 160.degree. C. can cause discolouration or degradation of the packaged product.
An object of the present invention is to provide an improved process and apparatus for use in packing commodities in bags of plastics material and sealing the bags with reduced chance of leakage from the sealed bags.